1. Field of the Invention
A toroidal-type continuously variable transmission and a continuously variable apparatus according to the present invention are used as a transmission apparatus for a vehicle or a transmission apparatus for controlling the operating speed of various industrial machines such as a pump.
2. Description of the Related Art
As a transmission constituting a transmission apparatus for a vehicle, a toroidal-type continuously variable transmission is known and is enforced in part of the vehicle industry. The toroidal-type continuously variable transmission enforced in part of the vehicle industry is a toroidal-type continuously variable transmission of a so called double cavity type in which transmission of power from an input part to an output part is executed in two systems which are arranged in parallel to each other. Such a toroidal-type continuously variable transmission is disclosed in many publications such as U.S. Pat. No. 5,033,322, U.S. Pat. No. 5,569,112 and U.S. Pat. No. 5,651,750 and is thus conventionally known. Description will be given below of the basic structure of this transmission with reference to FIG. 6.
The toroidal-type continuously variable transmission shown in FIG. 6 includes an input rotary shaft 1 serving as a rotary shaft. And, on the near-to-base-end (in FIG. 6, the left-side)portion and the near-to-leading end (in FIG. 6, the right-side) portion of the middle portion of the input rotary shaft 1, there supported input side disks 2a, 2b, respectively. The two input side disks 2a, 2b are supported on the input rotary shaft 1 through their respective ball splines 4, 4 in such a manner that their respective input side surfaces 3, 3, which are axial-direction one-side surfaces of the two input side disks 2a, 2b and are formed as toroid curved surfaces, are opposed to each other. Therefore, the two input side disks 2a, 2b are supported on the periphery of the input rotary shaft 1 in such a manner that they can be shifted in the axial direction of the input rotary shaft 1 and can be rotated in synchronization with the input rotary shaft 1.
Also, between the base end portion (in FIG. 6, the left end portion) of the input rotary shaft 1 and the outer surface of the input side disk 2a, there are interposed a rolling-bearing 5 and a pressing device 6 of a loading cam type. And, a cam plate 7, which constitutes the pressing device 6, can be driven and rotated by a drive shaft 8. On the other hand, between the leading end portion (in FIG. 6, the right end portion) of the input rotary shaft 1 and the outer surface of the other input side disk 2b, there are interposed a loading nut 9 and a countersunk plate spring 10 having large elasticity.
The middle portion of the input rotary shaft is penetrated through a through hole 13 formed in a partition wall portion 12 disposed in the interior of a casing 11(see FIG. 1 which shows an embodiment of the present invention) in which the toroidal-type continuously variable transmission. On the inside diameter side of the through hole 13, there is rotatably supported a cylindrical-shaped output cylinder 28 by a pair of rolling bearings 14, 14. On an outer peripheral surface of the intermediate portion of the cylindrical-shaped output cylinder 28, there is fixed an output gear 15. Also, on the portions of the two end portions of the output cylinder 28 that project from the two outer surfaces of the partition wall 12, there are supported output side disks 16a, 16b serving as inside disks in such a manner that they can be rotated in synchronization with the output cylinder 28 by spline engagement.
In this state, the output side surfaces 17, 17 of the output side disks 16a, 16b, which are the one-side surfaces of the output side disks 16a, 16b and are formed as toroid surfaces, are opposed to the input side surfaces 3, 3. Also, between the portions of the inner peripheral surfaces of the output side disks 16a, 16b that project from the end edge of the output cylinder 28 and the outer peripheral surface of the middle portion of the input rotary shaft 1, there are interposed needle roller bearings 18, 18. And, while loads applied to the output side disks 16a, 16b are being supported, the output side disks 16a, 16b can be rotated with respect to the input rotary shaft 1 and can be shifted in the axial direction of the input rotary shaft 1.
In the portions (cavities) of the periphery of the input rotary shaft 1 that are present between the input and output side surfaces 3, 17, there are disposed power rollers 19, 19 by two or more (generally, by twos or by trees). The power rollers 19, 19 are respectively supported by displacement shafts 21, 21, radial needle roller bearings 22, 22, thrust ball bearings 23, 23 and thrust needle roller bearings 24, 24 on the side surface portions of trunnions 20, 20 serving as support members, the peripheral surfaces 29, 29 of which are formed as spherical-shaped convex surfaces and are contacted with the input and output side surfaces 3, 17, in such a manner that they can be rotated as well as can be swung and shifted slightly. That is, the displacement shafts 21, 21 are respectively eccentric shafts arranged such that their respective base and front half sections are eccentric to each other; and, the base half sections are swingably and shiftably supported on the middle portions of the trunnions 20, 20 by another radial needle roller bearings (not shown).
The power rollers 19, 19 are rotatably supported on the front half sections of the above-structured displacement shafts 21, 21 by the radial needle roller bearings 22, 22 and thrust ball bearings 23, 23. Also, when the respective composing parts of the toroidal-type continuously variable transmission are elastically formed, the another radial needle roller bearings and thrust needle roller bearings 24, 24 allow the power rollers 19, 19 to shift in the axial direction of the input rotary shaft 1.
Further, in the case of the trunnions 20, 20, pivot shafts disposed on the two end portions (in FIG. 6, in the front and back direction) thereof are supported on support plates 25a, 25b (see FIGS. 1, 2 and 5 respectively showing the embodiments of the present invention) installed in the interior of the casing 11 in such a manner that they can be swung and can be shifted in the axial direction thereof. That is, the trunnions 20, 20 not only are supported such that they can be shifted in clockwise and counter-clockwise directions in FIG. 6 but also can be shifted by an actuator (not shown) in such a manner that they can be shifted in the axial direction of the pivot shafts (in FIG. 1, in the left-half-section direction, in FIG. 6, in the front and back direction; and, in FIGS. 1 and 2, in the right-half-section direction and, in FIG. 5, in the vertical direction)
When putting the above-structured toroidal-type continuously variable transmission into operation, the input side disk 2a is driven and rotated by the drive shaft 8 through the pressing device 6. Since this pressing device 6 drives and rotates the input side disk 2a while generating a thrust force in the axial direction thereof, while the input side disks 2a, 2b including the above input side disk 2a are being pressed toward the output side disks 16a, 16b, they are rotated in synchronization with each other. As a result of this, the rotational movements of the pair of input side disks 2a, 2b are transmitted through the power rollers 19, 19 to the output disks 16a, 16b, thereby rotating the output gear 15 connected to the output side disks 16a, 16b through the output cylinder 28.
When the toroidal-type continuously variable transmission is in operation, since the pressing device 6 generates the thrust force, there can be secured surface pressures in the respective contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17. Also, the surface pressures increase as the power (torque) to be transmitted from the drive shaft 8 to the output gear 15 increases. Thanks to this, there can be obtained a good transmission efficiency regardless of variations in the torque. Also, even in case where the torque to be transmitted is 0 or a very small, due to the countersunk plate spring 10 and a pre-load spring 26 which is disposed on the inside diameter side of the pressing device 6, in the respective contact portions, there can be secured a certain degree of surface pressure. Therefore, the torque transmission in the respective contact portions, just after the start of the operation of toroidal-type continuously variable transmission, can be carried out smoothly without incurring an excessive degree of slippage.
To change a transmission ratio between the drive shaft 8 and output gear 15, using an actuator (not shown), the trunnions 20, 20 may be shifted in the front and back direction of FIG. 6. In this case, the upper and lower (in FIG. 6) half sections of the trunnions 20, 20 are shifted by the same amount in the mutually opposite directions. These shifting movements of the upper and lower half sections of the trunnions 20, 20 change the direction of the force which is applied to the contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17 in the tangential direction thereof. Due to such tangential-direction force, the trunnions 20, 20 are swung about the pivot shafts which are respectively disposed on the two end portions of these trunnions 20, 20.
The swinging movements of the trunnions 20, 20 change the positions of the contact portions the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17 with respect to the diameter direction of these side surfaces 3, 17. As the contact portions are changed outwardly in the diameter direction of the input side surface 3 and inwardly in the diameter direction of the output side surface 17, the transmission ratio is changed to the speed increasing side. On the other hand, as the contact portions are changed inwardly in the diameter direction of the input side surface 3 and outwardly in the diameter direction of the output side surface 17, the transmission ratio is changed to the speed reducing side.
By the way, in the case of the conventional structure shown in FIG. 6, since, between the outer surfaces 27, 27 of the pair of output side disks 16a, 16b, there are interposed, in addition to the output gear 15, the pair of rolling bearings 14, 14 and partition wall portion 12 for supporting these rolling bearings 14, 14, the distance D27 between the two outer surfaces 27, 27 increases. This increases the axial-direction dimension of the toroidal-type continuously variable transmission, which in turn increases the size and weight of the toroidal-type continuously variable transmission. The increase in the size and weight of the toroidal-type continuously variable transmission is caused not only by such increase in the distance D27 but also by an increase in the axial-direction thickness of the output side disks 16a, 16b. The reason for this is as follows.
In the speed reducing state of the toroidal-type continuously variable transmission shown in FIG. 6, in a state where the peripheral surfaces 29, 29 of the power rollers 19, 19 are in contact with the near-to-outside-diameter portions of the output side surfaces 17, 17 of the output side disks 16a, 16b, they press against these output side surfaces 17, 17. Due to this, to the output side disks 16a, 16b, there is applied large moment with the spline-connected portions of the output disks 16a, 16b to the output cylinder 28 as the center thereof. In order not only to prevent the transmission ratio from being shifted but also to secure the durability of the output side disks 16a, 16b, it is necessary to restrict the elastic deformation of the output side disks 16a, 16b. And, for this purpose, it is necessary to increase the thickness dimensions of the output side disks 16a, 16b in the axial direction thereof to thereby enhance the rigidity of the output side disks 16a, 16b. For these reasons, in case where the axial-direction thickness dimensions of the output side disks 16a, 16b are increased, the size of the toroidal-type continuously variable transmission is accordingly increased in the above-mentioned manner.
On the other hand, in JP-A-2001-116097, there is disclosed a structure in which an integrally-formed output side disk is rotatably supported on the periphery of the middle portion of an input side rotary shaft by a pair of radial needle roller bearings and a pair of thrust needle roller bearings. According to the structure disclosed in the above-cited publication, not only because the partition wall portion 12 can be omitted from the conventional structure shown in FIG. 6 but also because the axial-direction dimensions of the output side disks can be reduced, the size and weight of the whole of a toroidal-type continuously variable transmission can be reduced.
However, in the case of the thrust needle roller bearings employed in the last-cited publication, since heat is generated excessively due to slippage friction in the rolling contact portions between the rolling surfaces of the respective needle rollers thereof and their mating raceway surfaces, it is difficult to use the thrust needle roller bearings in a state where a preload is applied. In other words, in a case where the lives of the thrust needle roller bearings should be secured sufficiently, the thrust needle roller bearings must be used in a state where they have a positive clearance between them. For this reason, it is difficult to restrict the axial-direction position of the output side disk strictly and thus there is a possibility that the contact positions between the output side surface of the output side disk and the peripheral surfaces of the respective power rollers can be shifted slightly.
In case where the contact positions between the output side surface of the output side disk and the peripheral surfaces of the power rollers are shifted for such reason, there arises a possibility that, in the rolling contact portions of these mating surfaces, there can be generated side slippage, the trunnions supporting the power rollers can be rotated about their respective pivot shafts, and thus the transmission ratio of the toroidal-type continuously variable transmission can be varied unexpectedly. Such state is undesirable because it gives a driver a strange feeling. Especially, in the case of a continuously variable transmission apparatus in which a toroidal-type continuously variable transmission unit and a planetary-gear-type transmission unit are combined together to thereby realize an infinite transmission ratio, in a state where a large torque passes through the toroidal-type continuously variable transmission unit, the transmission ratio must be controlled delicately. Therefore, it is especially undesirable that the transmission ratio is changed unexpectedly.